Evidence of strong indium segregation in MOCVD In x Ga 1-x N/GaN quantum layers
- PDF / 4,136,999 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 107 Downloads / 235 Views
Y10.55.1
Evidence of strong indium segregation in MOCVD InxGa1-xN/GaN quantum layers Grzegorz Maciejewski1), Grzegorz Jurczak1), Sławomir Kret2), Paweł Dłużewski1) and Pierre Ruterana3) 1
Institute of Fundamental Technological Research PAS, Świętokrzyska 21, 00-049 Warsaw,
Poland 2
Institute of Physics PAS, Al. Lotników 32/36, 02-668 Warsaw, Poland
3
SIFCOM, UMR6176, ENSICAEN-CNRS, 6 Bd Maréchal Juin, 14050 Caen Cedex, France
ABSTRACT An investigation of 1-5 nm in diameter indium rich clusters in MOCVD InxGa1-xN/GaN quantum well is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with the Finite Element Method (FEM) for the calculation of thin foil relaxation and for image simulation. The measurement of the tetragonal distortion from HRTEM images is a useful tool for the determination of chemical composition in heterostructures. However, for a correct interpretation of the measured lattice distortion on HRTEM images, one needs to take into account the strain averaging across TEM sample and inhomogeneous relaxation of the sample. As a first step, 3D FEM simulation of the relaxation process as a function of the position of indium rich cluster relative to the foil surface is performed. Next, the calculated 3D displacement field is used to simulate the HRTEM images. The results clearly show that the magnitude of the strain field depends on the cluster position. It is concluded that the HRTEM images of indium rich clusters can differ even for the same indium content due to different positions of the clusters.
INTRODUCTION The optical devices based on GaN/InxGa1-xN/GaN quantum well (QW) structure operate at room temperature with a high density of defects inside the layers. The observations suggest that their high-efficient luminescence may result from the presence of the indium rich clusters inside QWs area [1], which behave like quantum dots. Even though the optical and electrical properties of the GaN/InxGa1-xN/GaN QW’s have been investigated quite well, the mechanism of the light emission is not yet clearly understood. Narukawa et al. [1], based on TEM and EDS, suggested that indium rich cluster is an electron trap and centre for a radiative excitonic recombination. Kisielowski et al. [2], using pattern recognition on HRTEM images, have shown that the indium may segregate into 1-3 nm diameter areas inside the QW. Ruterana et al. [3], based on a strain distribution extracted from HRTEM images and 2D FEM modelling, have shown that the In composition fluctuation areas may depend on the deposition technique. Recently, Watanabe et al. [4] presented an atomic-scale compositional analysis by high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). These reports agree quite well on the
Y10.55.2
nanometre scale for the In composition fluctuation inside the QWs. During last few years, there has been a considerable interest in studying the strain field of a GaN/InxGa1-xN/GaN quantum well (QW), because of strongly influence on funct
Data Loading...
